1. Field of the Invention
The present invention relates to a process for producing an olefin polymer by use of a polymerization catalyst comprising a metallocene, an organoaluminum compound, and an ionizable ionic compound.
The present invention also relates to a process for producing an olefin polymer by use of a polymerization catalyst comprising an ionic metallocene and an organoaluminum compound.
2. Description of the Related Art
The polymerization of ethylene or an .alpha.-olefin by a low-pressure Ziegler process is well known in the art. The catalyst therefor is prepared by mixing an organometallic compound or a hydride of an element of 1A to 3A Group of Periodic Table with a compound of a transition metal (an element of 3B to 2B Group of Periodic Table), and treating the mixture in suspension or solution or in the absence of a diluent or a solvent.
Known special kinds of catalysts active for olefin polymerization include combinations of aluminoxane with a cyclopentadienyl derivative of a metal of 4B Group such as titanium, zirconium, and hafnium, or the like. Such catalysts are disclosed in the literature "Ziegler-Natta catalyst and polymerization", Academic Press, New York (1979); Adv. Organomet. Chem. 1899 (1980); and so forth. Such catalysts advantageously exhibit high catalytic activity and are capable of producing stereoregular polyolefins. However, these catalyst have not been used in industrial polymerization, mainly because the aluminoxane cannot readily be synthesized in a reproducible state and therefore the catalysts and the polymers cannot be prepared with reproducibility.
A catalyst which offsets such problems is disclosed in Japanese Patent Application Laid-Open No. Hei-3-207704, which describes a bis(cyclopentadienyl)metal compound prepared by reaction of a metallocene with ionic compound and the use of the resulting complex as a polymerization catalyst. This catalyst, however, is not satisfactory in the catalyst activity.
The inventors of the present invention have made comprehensive study to solve the above problems of the olefin polymerization catalyst employing a metallocene and an organoaluminum compound, and completed the present invention.